1. Field of the Invention
The present invention relates to a Method, Process or System for processing and treating an aqueous radioactive liquid in a nuclear reactor for the purpose of removing radioisotopes or radioactive metal ions and particulate so as to significantly reduce the volume of the radwaste for use, disposal or storage, and to generate only one additional stream containing the water, salts and non-radioactive components in a form that can safely be returned to the environment separate and apart from the nuclear reactor site to protect ground and ground waters.
2. Background Information
The liquid radwaste (LRW) systems in commercial nuclear power plants and utilities have used conventional demineralization to provide discharge wastewater that attempts to meet both NRC and waste quality requirements for radioactive isotopes and RCRA elements. Plants have attempted to stay below regulatory discharge requirements by using demineralizer (ion exchange) technology where the principal components have included conventionally positioned demineralizing systems consisting of tanks, essential piping, pumps and valves. Liquid wastes generated in using such past conventional setups have required further cleanup or treatment before other use in a different area of the plant and were not capable of effectively treating or processing radwaste liquids to quality grade water permitting discharge back to the outside environment.
More recently other factors have come into play. The potential contamination of rivers, lakes, bays and estuaries by plant discharges has resulted in increased nuclear insurance rates, and attention by industry peer review and audit groups, and public attention by various activist groups, has motivated utilities to continually improve environmental performance. The emphasis has therefore been on reducing releases of the main or primary gamma, beta and alpha activity contributors of cesium, cobalt iodine and others substantially below regulatory level for liquid releases to the environment.
As discharge of radioisotope emitters was reduced, secondary isotopes such as antimony and iron, previously masked or difficult to detect, became more focused. It was found that Iron isotopes 55 and 59 were not readily removed by filtration and ion exchange. Therefore, a need for a more effective removal processing before discharge became necessary.
Tritium isotopes were more readily detected but virtually impossible to separate from the process stream. Therefore, plants have been evaluating the possibility of recycle of liquid streams back to the plant for further use instead of being discharged with tritium to the environment.
Prior to the present invention, mechanical filtration and ion exchange technology were only marginally capable of meeting reduced gamma discharges, effective removal of secondary isotopes for discharge, or production of the high quality water required for recycle to allow retention of tritium.
Additionally, aspects of the past technology in dealing with RCRA wastewaters, and recycle applications containing regulated chemicals being permitted only to be discharged in limited amounts, have been sorely missing and urgently needed.
In recent decades various membrane separation processes have been developed and utilized in the field of potable water purification; and more recently in the treatment of various process and waste liquors. Some of the membrane processes are capable of removing both dissolved and particulate contaminants. The best known and most utilized membrane processes in the field of water and wastewater treatment are those utilizing pressure gradients as the process driving force. These processes include reverse osmosis, nanofiltration, ultrafiltration and microfiltration.
Conventional reverse osmosis or RO has been used in the past in certain industrial settings; having been applied to separation, concentration of product streams, and wastewater treatment. More specifically, the past conventional RO technology setups have been used for removal of radionuclides from low level liquid wastes such as waste streams at nuclear power plants. In this regard, conventionally placed RO systems have been used in the nuclear industry as a part of an overall liquid waste treatment system.
Importantly, in its conventional use and positional placement, RO was set up and placed in a position in a system or process ahead or in front of a polishing demineralization treatment, in a configuration referred to as RO-IX. In this configuration, the RO separated the raw process stream into two distinct streams: 1) the permeate (clean) and 2) the reject (dirty) stream. The clean stream, containing reduced concentrations of impurities after one or two passes, still often required polishing with downstream ion exchange media to meet quality requirements for either recycle or discharge. The reject stream, containing a high fraction of the raw stream constituents, was then conventionally subject to further processing, for example, evaporating or drying to dried solids. In this configuration, 90% to 99.9% of the waste stream contaminants were rejected by the RO and the balance removed by the downstream IX polisher.
A number of problems and deficiencies in this process setup and positional configuration have been identified. When presented with a high concentration of contaminants in the raw waste stream, a higher than desirable concentration of contaminants pass through the membrane, often requiring multiple RO passes and extensive ion exchange polishing to produce an acceptable permeate, thus resulting in increased capital equipment and operating costs and increased consumption of ion exchange resin to polish the permeate. In some instances, the RO concentrated raw stream contaminants to near their solubility limits. The volume of the reject had to be increased to preclude precipitation on the membrane and their fouling. The need for these process conditions, to effect adequate cleanup, resulted in increased equipment and operating costs, larger equipment footprint and increased resin consumption and further processing of increased reject volumes.
Additional problems in this past technology setup were found to occur with respect to utilization of the reject stream, which generally represented 2-15% of the feed stream volume. It was found that it was required to deal with such a waste stream because it contained a number of undesirable elements. In non-nuclear applications these waste streams could often be discharged to sanitary sewers or even returned to the original body of water. However, in nuclear applications, as preferred in the present invention, the reject contained radioactive isotopes that were required to be sent to special disposal facilities in a stabile or non-mobile form. Since water or substantially aqueous volumes were not regarded as an acceptable form, the water had to either be solidified or evaporated to leave dry or dirt-like solids. Since these volumes were significant the cost was found to be high, and sometimes prohibitive. As was the case before and now, often suitable locations to provide drying or solidification are not easily found in nuclear plants. In this regard, it is important to note that the present invention and method totally eliminates or substantially minimizes the need to dispose and treat the reject stream by evaporation, solidification or off-site transportation. The ion exchange media, as positioned in the invention steps removes the concentrated ions in the reject which are captured in the polishing phase or step of the invention. This prevents the osmotic pressure from increasing and the efficiency of the RO in the invention from decreasing. This means that potentially no dry solids will be generated. Therefore, this reduces the overall waste volume to be disposed in light of the fact that greater than 99% of the waste is typically boron salts when dry solids are produced. Previous systems in the past technology all generated continuous reject streams that had to be retreated. At best, these could only be recycled a short period of time prior to the results of the system deteriorating or degrading below acceptable levels. Likewise, the reject stream suffered shortcomings from this conventional processing configuration. The reject stream, generally representing 2-15% of the feed stream volume, contained 90% to 99% of the contaminants presented to the RO in the raw waste stream. Some constituents may have been near their solubility limits, and thus could not be reprocessed through the RO a second time. If the reject was returned to the plant, the high concentration of contaminants was undesirable. In the past, in the instance and application of radioactive waste, if the reject was further processed for disposal, the high concentration of contaminants might cause elevated radiation doses to personnel. In other instances, the high concentration of specific isotopes might cause an increase in waste classification from the desirable low Class A classification to Class B and C, resulting in more onerous packaging, shipping and disposal requirements. In past occurrences, the concentration of certain radioactive constituents caused the classification to be greater than Class C (GTCC), which precluded or denied disposal by any means.
Additionally, in instances where the reject volume was increased to preclude exceeding the solubility of raw waste stream constituents to prevent membrane fouling, the greater volume of reject resulted in increased secondary processing costs for such treatment processes as evaporation, drying or solidification. The increased reject volumes and secondary processing costs reduced the economic viability of the conventional RO-IX positional setup and process configuration.
Also, in non-nuclear applications these concentrated reject constituents precluded normal discharge to sanitary sewers, or return to the original body of water. If these existing permeate and reject stream problems could be solved, substantial operational and economical benefits would be realized, thus enhancing the value and utility of RO as a purifying method, including RO treatment of nuclear waste or process streams. Therefore, the teachings of the present invention were developed to overcome the problematic issues in the past technology regarding these matters, particularly with regard to processing and treatment of heat transfer and other radioactive liquids the subject of chemical change and reaction in a nuclear reactor.
Further, in this regard, in distinguishing over the past technology in this area, the present invention treats nuclear reactor cooling water or a heat transfer water from nuclear reactor cycles to remove radioactive metal ions. The present invention is designed to pass through as many of the nonradioactive components in the water as possible for the purpose of minimizing the quantity of radwaste generated for evaluation and other uses. By utilizing the gross demineralizer means of the present invention for active processing by ion exchange of the (AF) in front of the invention's polishing reverse osmosis (RO) step, the ionic exchange media of the gross demineralizing step of the invention accumulates more radioactive metals and the following (RO)-polishing step and means is protected from accumulating greater amounts of radioactive dose and emitting greater amounts of gamma emissions from such radiation to personnel working in the area.
Utilizing the ion exchange or ion capture of demineralization of the present invention in front of the RO also maximizes the utilization of the ion exchange media as the loading of as much radioactive metal ion as possible occurs. Using the ion exchange media after the RO, as done in prior art technology, often meant less than 60-70% utilization of the media and much lower loading of radioisotopes.
Additionally, Boron passage is maximized utilizing the present invention while past technology, such as Dagard (U.S. Pat. No. 5,082,618) entitled “Method and Device For Modifying the Concentration of the Soluble Poison Contained in the Cooling Fluid of the Primary Circuit of a Nuclear Reactor”, decreased the passage of Boron. Importantly, Salts and nonradioactive metals are passed on through the present invention as much as possible to reduce the volume of radwaste generated. In this regard the present invention is utilized as the sole release point for liquid effluents from a nuclear power plant. Liquids must be released as a license condition for the operation of the plant. B10 (also referenced herein as B10 and boron-B10) is consumed as a neutron absorption agent to control the nuclear reaction and is converted to B11 (B11). While references such as the Dagard patent teach retaining B11 the present invention's method functions to remove the B11 and assist revitalization of the neutron absorption capacity (poison) of the reactor coolant with the addition of fresh B10.
To restate, though Dagard relates to PWR nuclear plants, its teachings clearly address the removal of boric acid (which it places within part of its definition or terminology as “poison”) from the primary water of the plant. Distinguishably, the present invention addresses the passage of boric acid (the Dagard ‘poison’) through the membranes so as little as possible of the boric acid is removed. The clear intention of the present invention is not to modify the concentration of the boric acid, but to assure its element form as Boric Acid and pass it through along with salts and other non-radioactive components through the method's system as part of the environmentally protective quality water to be released to the environment as the sole aqueous waste stream; and, in so doing, to reduce the radwaste volume for use, storage or disposal without the need of past practices of drying and/or solidification to do so. Dagard addresses ion exchange, but only for the removal of boric acid regarding which the present method emphasizes minimization and elimination for so doing. Dagard also teaches the use of ammonia which would be detrimental to the present method because it causes decreased efficiency of the RO and demineralizers. Also, one of the express primary purposes of the present method and invention in removing radioisotopes or radioactive metal ions is not addressed in Dagard in any manner; nor would it be correct to assume in their disclosure that it would be obvious to address such a purpose.
Further, in non-analogous technology in relation to that of nuclear reactor liquid treatment, the Al-Samadi patent (U.S. Pat. No. 6,113,797), entitled “High Water Recovery Membrane Purification Process” utilizes a two stage RO process with pretreatment limited to filtration to deal with scaling elements such as calcium and magnesium. Distinguishably, the present invention does not have to deal with scaling issues since it utilizes, as a part of it's demineralization step, ion exchange to remove scaling metals and filtration to remove solids prior to the polishing RO step of the invention, along with serving the other purposes in the invention of aiding reduction of the amount of radioactive isotopes passing therethrough. The present invention further distinguishes over Al-Samadi in discharging 100% of the influent water entering the present method in the aqueous radioactive liquid as purified water, without the need for a separate waste liquid stream which could not be released to the environment.
Also, the Rosenberger invention (U.S. Pat. No. 7,067,057), entitled “Fluid Conveyed Material Collection System”, discloses a device which does not teach the use of ion exchange in advance of RO, as the present invention does. It also teaches the use of further processing of RO concentrate to either dry solids or other solidification methods in great distinction to the present invention. Rosenberger also appears to require the use of precipitants. Rosenberger also teaches ‘backflushing” which is not present and would achieve no purpose in the present invention in that it causes much additional ‘tankage’ and process interruptions that is unneeded and would be a great disadvantage if used in the present invention. Rosenberger also teaches that one or more streams from membrane processes require additional outside processing to bring the final materials to a disposable and dischargeable state. Also, in relation to the teachings of the present invention, the Rosenberger device's use of evaporation, electrode coagulation, centrifugation and precipitating agents makes the use of this device a more complex and capital intensive process. In this regard, at least two membrane systems are required for most applications set forth for the Rosenberger device.
Further in divergent and non-analogous technology in relation to treatment of a nuclear reactor liquid, the Mukhopadhyay patent (U.S. Pat. No. 6,537,456) entitled “Method and Apparatus For High Efficiency Reverse Osmosis Operation”, does not disclose use of any recycle of its subject reject stream. Mukhopadhyay simply sets forth a process employing a very standard approach to RO which would not address the problems of seeking to emit a single waste stream of quality water to the environment as does the present invention and method. Though it appears that the Mukhopadhyay process employs the use of ion exchange media both in front and after the RO disclosed the reference does not in any way provide for recycle of any reject stream to the front of the system, as the present invention does to achieve the important purpose of improving the filtration of radioactive contaminants and allowing the salts and non-radioactive components to move through to ultimate clean water environmental disposal while allowing the volume of the radwaste to be significantly less for storage, use or disposal. In a similar regard, this patent reference teaches use of the RO as a gross separator rather than the specific relegation and limitation as in the present invention method to a “polisher” and sole use in a “polishing” capacity. Also, very importantly, Mukhopadhyay teaches the ‘minimization’ and strict limitation of boron and silica passage through its process, where the method of the present invention seeks to ‘maximize’ the passage of these substances for important object and purpose of the present invention as indicated to uniquely and significantly minimize the radioactive waste volume for later use, storage or disposal. Mukhopadhyay makes no attempt to address this problem and must be considered significantly non-analogous to the operation and chemical processes of a nuclear reactor for this reason among others. In dealing with chemical nuclear reactor processes in the past technology the reject volume issuing from a nuclear reactor posed a significant waste volume problem that had to normally be disposed in a nuclear application setting through either drying or solidification. The present invention uniquely and importantly provides a novel method, which might normally be unexpected by simply looking at the alignment of elements utilized in the present method and invention, to significantly solve the radioactive waste volume problem while still providing only one aqueous stream to be returned to the environment rather than to another location at the nuclear reactor site or for logistical placement, storage or disposal at a non-environmental location.
Each of the references above; or those like them, but also distinguishable; fail to teach important aspects of the method of the present invention. For example, each of the analogous or non-analogous references in the past technology failed to recognize the usefulness of using a more broad spectrum ion exchange media in front of the RO to capture all of the ions in a concentrated form such that the RO could be subsequently used as a polishing method step rather than as a primary separator. All of the references in the past technology in this or any remotely related area used the RO as a primary separator rather than as a polisher where the RO reject was then at a concentration that the primary ion exchange beds could remove it to reasonable levels. All of the other references also required significantly more equipment to provide the same permeate results, and all had a secondary waste other than membranes or media regarding which they had to account for and dispose.
Accordingly, it is an object of the present invention to provide a permeate stream or first liquid volume and a reject stream or second liquid volume, so that the reject stream is recycled back to the front of it's own system process of which it is a part of, or back to the nuclear reactor plant source, so that the repetitive effect of the invention's non-conventional gross demineralizer step in the present invention can be achieved; i.e., the removal percentage of demineralizers employed in such a system is great enough; to prevent excess buildup of most all isotopes and other fouling chemicals.
It is also an object of the invention, in preferred embodiments, to utilize a method and system in proximate location to the end of its novel gross demineralizer of (AF) processing step to specifically polish radwaste or radioactive wastewater from a radwaste system of a nuclear reactor of the remaining isotopes and other dissolved and colloidal materials, when present.
It is a further object of the invention to maximize boron control. In the present invention this is accomplished by passage or recycle through the invention's non-conventional polishing RO process step. This is done to meet the requirements necessary for discharge of an aqueous wastestream directly to the environment apart from the nuclear reactor site or recycle within the steps of the present method. This is accomplished, in part within the present method, by raising or lowering the pH for the purpose of altering the characteristics of the aqueous wastestream to assure formation and passage of boric acid with the waste stream of the invention released to the ambient environment outside a nuclear reactor site.
A further object exists in facilitating the periodic use of a chemical treatment system to precipitate the silica in the system, or capture the silica by selective ion exchange when required.
Further objects and advantages of the present invention include utilizing the RWRO post IX polisher therein of the invention; the advantageous use of carbon filters and ion exchange resins as good removal media for TOC found in the feed water; the reduction of TOC fouling of RO membranes; the use of deep bed carbon filtration ahead of demineralizers to reduce fouling as compared to mechanical filters conventionally used ahead of RO systems; the reduction of TSS fouling of RO membranes; the reduction of dose rate on RO system and membranes; the quality of the water discharged to the environment; and the maximization of resin utilization by exposing the resin to higher influent activity concentration and retaining resin until completely depleted; and the utilization of acid conditions by cation resin (i.e., hydrogen form cation resin before the RWRO) to reduce pH adjustment and improve BA passage.
Additional objects and benefits include: the reduction of volume rejected and returned to the nuclear reactor plant; the reduction in the waste classification of concentrates and/or resulting dried solids; the maximization of resin utilization by exposing resin to a higher influent activity concentration; the prevention of the return to the nuclear reactor plant, or environmental discharge, of difficult to remove isotopes; the facilitation of scavenging for and selective capturing or removal of targeted isotopes, such as antimony, Cobalt, Cesium, Iodine, Tellurium, Manganese, Iron, Silver, Chromium, and Niobium, and those related thereto in the nuclear cooling fluid and radwaste processes.
In a smaller waste stream, then provided as a result of the present process; and the decrease on osmotic load through the use of increased reject flow rate.
It is a further object of the invention to more effectively and efficiently provide for reduced radioisotope discharges, removal of secondary isotopes for discharge, and production of high quality water for recycle within the invention's process and release to the environment to allow retention of tritium.
It is a further object to provide effective boron recycle or for recycle of other non-radioactive elements for further processing within the invention's system.
A further object exists in providing a system which has application in dealing with RCRA wastewaters and recycle of regulated chemicals that can be discharged only in limited quantities.
It is the object of the present invention to provide a methodology of applying RO and ion exchange (IX) in such a functional and positional manner as to create more favorable operating conditions and performance of the RO and demineralizer (IX) by situating the demineralizer system ahead of the RO in a configuration referred to as IX-RO. In so doing, the RO acts as a polisher in follow-up to the gross demineralization step in the system. In the IX-RO configuration, often 90% to 99% of the contaminants will be removed by the IX system in advance of the RO polisher. A secondary configuration provides demineralization of the reject stream to further strip undesirable species from the reject before recycling or processing of the reject stream. These configurations result in improved RO performance and improved permeate and reject stream quality and conditions.
Another object and advantage of the invention includes IX scavenging of raw waste stream constituents that, when concentrated in the RO, could precipitate and foul the RO membranes. Reduction of such agents permits controlling the reject flow rates to meet the hydraulic needs of the membranes instead of adjustment to control internal RO precipitation, where such adjustments would result in reduced reject flow rates and volumes that must be recycled or treated.
A further object and advantage is served by IX scavenging of raw waste stream constituents, resulting in reduced concentration of contaminants in the reject stream. This favorable condition reduces the inventory of contaminants recycled within the process system itself. The lower concentration of reject contaminants permits reprocessing through the IX-RO system with reduced concern of precipitation.
Another object and advantage of the invention is set forth by IX scavenging of raw waste stream constituents, including reduction in the concentration of key isotopes that affect waste classification for waste packaging, shipping and burial. Reduction of these isotopes in the raw waste stream, results in advantageous and supportive reduction in the reject stream subject to secondary processing for disposal.
A further object and advantage of the invention is served by IX scavenging of raw waste stream constituents, including radioactive isotopes, to reduce mechanical entrapment of isotopes in the RO membranes and process equipment system.
Accordingly, the lower radioactive dose rates achieved through using the present method in nuclear reactor liquids to change their chemical makeup, volume and packaging reduce exposure to operating personnel. This also reduces the frequency of, or need for, cleaning RO membranes, which would normally be needed to address and lower accumulated substances causing radioactivity. This facilitates avoidance of exposure to personnel, which would otherwise be necessary for handling and packaging of expended membranes. Further objects and advantages of the invention are served by IX scavenging, i.e., gross demineralizing of contaminants from the reject stream to reduced isotopic content, resulting in reduced dose buildup during secondary processing within the present invention of the reject stream or volume. Particular isotopes; for example, cesium 137, cobalt 60, carbon 14, iron 55, nickel 63 and antimony 125, when present in elevated concentrations, may result in elevated waste classification imposed by the Nuclear Regulatory Commission and other governmental and regulatory bodies. This results in more onerous packaging, shipping and burial requirements. Scavenging, by IX-gross demineralizing, for these and other select isotopes from the reject stream enables maintenance of Class A classification, resulting in reduced handling and disposal costs.
Additional objects and advantages of the invention include IX scavenging of raw waste stream constituents, to reduce the concentration of contaminants presented to the RO. Lower RO influent contaminates results in reduced contaminant concentrations in the RO permeate. This reduces or eliminates the need for additional RO passes to effect cleanup of the process stream; or, in turn, reduces or eliminates the need for post-RO IX polishing of the permeate for discharge or recycle.
Other objects and advantages of the invention are served by IX scavenging of raw waste stream constituents to reduce the concentration of contaminants presented to the RO. This results in contaminants being affixed or captured by the IX-gross demineralizing step or being affixed or captured by the IX system of the invention. This is a more favorable and efficient waste form for handling, packaging and disposal.
An additional object of the invention, and advantage served, includes IX scavenging of raw waste stream constituents, where the RO acts as a polisher. This maximizes IX resin utilization by permitting IX beds to remain in service well beyond normal chemical depletion. Ionic leakage from partially or fully chemically depleted IX bed is either captured by downstream IX bed; or when passed to the RO, is rejected to the reject stream. This contribution to the reject stream, in this case, is sufficiently small, often 1% -2% of the influent stream contaminate total. This does not materially or adversely affect the quality and secondary processing of the reject stream.
A further object, and advantage, of the invention lies in maximizing resin utilization and consumption reduction wherein the IX beds are exposed to the maximum concentration of contaminants of the raw process stream. This results in a more complete utilization of the exchange capacity of the resin and higher exchange equilibrium. All of these things result in higher waste loading and reduced resin consumption, compared to IX performance when positioned in the dilute contaminant stream of the RO permeate as was the case in the past conventional technology.
Another object of the invention is to set forth IX positioning in advance of the RO to enhance boron passage through the RO membranes. This enhanced passage is affected by pH reduction as the process stream passes through hydrogen form cation resin or by addition of acids, such as sulfuric or hydrochloric, to the process stream. Passage of a greater fraction of the boron to the permeate permits recovery of boron in the permeate and reduces the concentration in the reject stream. This avoids RO operating limitations imposed by the potential for precipitation of boron; and also reduces the resulting dried waste volumes due to reduced boron content. In the alternative, when minimizing boric acid in the permeate; the pH can be increased by passing the process stream through a hydroxide form anion resin or by addition of a basic solution such as sodium hydroxide.
A further object includes setting forth a system where the IX position is placed in advance of the RO, in facilitating the periodic use of a chemical treatment system to precipitate silica in the IX system, or for capturing the silica by selective ion exchange when required or appropriate. An additional object is to set forth in the present method and system where the IX position is placed in advance of the RO in facilitating improved TOC removal from carbon filters downstream. When employed such carbon filters have the primary purpose in filtration and TOC removal. The use of IX aids in removal of that fraction of TOC that successfully transits the carbon filter. This protects the downstream RO from TOC contamination (a primary membrane fouling mechanism).
Yet a further object of the invention includes presenting a system and process that provides the further advantage of utilizing the RWRO as a post IX polisher in the invention. Other related advantages, in this regard, include the advantageous use of carbon filters and ion exchange resins as removal media for TOC found in the feed water; the reduction of TOC fouling of RO membranes; the use of deep bed carbon filtration ahead of demineralizers to reduce fouling as compared to mechanical filters conventionally used ahead of RO systems; the reduction of TSS fouling of RO membranes; the reduction of dose rate on RO system and membranes; the reduction of activity returned to the plant or discharged to the environment; the maximization of resin utilization by exposing the resin to higher influent activity concentration and retaining resin until completely depleted; and the utilization of acid conditions when needed.
It will, therefore, be understood by those skilled in these technologies that substantial and distinguishable device, process and functional advantages are realized in the present invention over the past conventional technology with regard to processing, treating, packaging and chemically affecting a radwaste liquid in a nuclear reactor. It will also be appreciated that the efficiency, flexibility, adaptability of operation, diverse utility, and distinguishable functional applications of the present invention all serve as important bases for novelty of the invention, in this field of technology.